It is a fundamental aim in developing internal combustion engines to minimize fuel consumption, with increased overall efficiency being at the forefront of the efforts made. Fuel consumption, and hence efficiency, is problematic, especially in the case of spark-ignition engines, e.g. in the case of internal combustion engines with applied ignition. The reason lies in the fundamental operating method of the spark-ignition engine. Load control is generally performed by a throttle valve provided in the intake system. By adjusting the throttle valve, the pressure of the induced air behind the throttle valve can be reduced to a greater or lesser extent. The further the throttle valve is closed, e.g. the more it blocks the intake system, the greater is the pressure loss in the induced air across the throttle valve and the lower is the pressure of the induced air downstream of the throttle valve and ahead of the inlet to the at least two cylinders, e.g. combustion chambers. Given a constant combustion chamber volume, the air mass, e.g. quantity, can be adjusted by the pressure of the induced air. This also explains why quantity control proves disadvantageous precisely in part-load operation, since low loads use a high degree of throttling and pressure reduction in the intake system, thereby causing a rise in exhaust and refill losses with decreasing load and increasing throttling.
Another possibility for optimizing the combustion process in a spark-ignition engine is to use an at least partially variable valve gear. In contrast to conventional valve gears, in which both the stroke of the valves and the timings are invariable, these parameters that influence the combustion process and hence fuel consumption can be varied to a greater or lesser extent by variable valve gears. Throttle-free and hence loss-free load control is possible merely through the possibility of varying the closing time of the inlet valve and the inlet valve stroke. The mass of mixture flowing into the combustion chamber during the intake process is then controlled not by a throttle valve but by way of the inlet valve stroke and the opening duration of the inlet valve. However, variable valve gears are very expensive and are therefore often unsuitable for use in production vehicles.
Another possible solution for dethrottling a spark-ignition engine is offered by cylinder shutdown, e.g. the switching off of individual cylinders in certain load ranges. The efficiency of spark-ignition engines in part-load operation may be increased, by partial shutdown, since switching off a cylinder of a multi-cylinder internal combustion engine increases the loading of the other cylinders that are still in operation, given a constant engine output, and therefore the throttle valve may be opened further to introduce a larger air mass into said cylinders, the overall result being dethrottling of the internal combustion engine. During partial shutdown, the cylinders that are continuously in operation operate in the range of higher loads, at which specific fuel consumption is lower. The load population is shifted toward higher loads. The cylinders that continue to be operated during partial shutdown furthermore have increased mixture formation and tolerate higher exhaust gas recirculation rates by virtue of the larger air mass or mass of mixture supplied.
The cylinders that continue to be operated during partial shutdown furthermore tolerate higher exhaust gas recirculation rates by virtue of the larger fuel mass supplied, e.g. by virtue of the richer mixture. As regards wall heat losses, the same advantages are obtained as with spark-ignition engines, and therefore attention is drawn to the corresponding explanations.
Partial shutdown in the case of diesel engines is also intended to prevent the fuel/air mixture from becoming too lean in the course of quality control as the load decreases, due to a reduction in the fuel quantity employed.
However, the multi-cylinder internal combustion engines featuring partial shutdown which are known, and the associated methods for operating said internal combustion engines, have significant potential for improvement, as will be explained briefly below, using a diesel engine by way of example. If the fuel supply to the cylinders that can be switched off is suppressed, e.g. shut down, for the purpose of partial shutdown in the case of a direct heat-injection diesel engine, the cylinders that have been switched off continue to take part in the exhaust and refill process if the associated valve gear of said cylinders is not deactivated or cannot be deactivated. The exhaust and refill losses generated in this case reduce the improvements as regards fuel consumption and efficiency which are achieved by partial shutdown and counteract said improvements, with the result that the benefit of partial shutdown is at least partially lost, that is to say that, overall, partial shutdown actually involves a less significant improvement.
In practice, it is not expedient to remedy the disadvantageous effects described above by providing switchable valve gears since switchable valve gears, like variable valve gears, are very expensive. Moreover, switchable valve gears would lead to further problems in the case of internal combustion engines pressure-charged by exhaust turbocharging since the turbine of an exhaust turbocharger has to be designed for a particular exhaust gas quantity and hence also for a particular number of cylinders. If the valve gear of a cylinder that has been switched off is deactivated, the total mass flow through the cylinders of the internal combustion engine decreases owing to the lack of mass flow through the cylinders which have been switched off. The exhaust gas mass flow passed through the turbine decreases and, with it, the turbine pressure ratio. The result is that the boost pressure ratio likewise decreases, e.g. the boost pressure falls, and a small amount of fresh air or charge air is fed or can be fed to the cylinders which continue in operation. The low charge air flow can also lead to the compressor operating beyond the pulsation limit.
The effects described above lead to a restriction in the application of partial shutdown, namely to a restriction of the load range in which partial shutdown can be employed. The reduced charge air quantity which is fed to the cylinders that are in operation during partial shutdown reduces the effectiveness or quality of combustion and has a disadvantageous effect on fuel consumption and pollutant emissions.
The boost pressure in the case of partial shutdown and hence the charge air quantity fed to the cylinders that continue in operation could be increased, for example, by a small turbine cross section design and simultaneous exhaust gas blowoff, which would also expand the load range relevant to partial shutdown again. However, this procedure has the disadvantage that the pressure-charging behavior is inadequate when all the cylinders are operated.
The boost pressure in the case of partial shutdown and hence the charge air quantity fed to the cylinders which continue in operation could also be increased by providing the turbine with variable turbine geometry, which allows adaptation of the effective turbine cross section to the instantaneous exhaust gas mass flow. In that case, however, the exhaust back pressure in the exhaust system upstream of the turbine would simultaneously increase, leading in turn to higher exhaust and refill losses in the cylinders that continue in operation.
The inventors herein recognize the above mentioned disadvantages and disclose an internal combustion engine with greater efficiency. In the case of the internal combustion engine according to the disclosure, the charge air supply to the cylinders that have been switched off, e.g. the charge air quantity supplied during partial shutdown, can be reduced and controlled, or even cut off if appropriate, without fitting the switchable cylinders with switchable valve gears, which give rise to high costs. For this purpose, a throttling element is provided in the intake line of each cylinder which can be switched as a function of load. The flow cross section of the intake line can be varied, in particular reduced, by actuating said throttling element, thereby enabling the charge air quantity fed to the at least one cylinder that has been switched off during partial shutdown to be adjusted, metered and controlled.
The charge air supply can be reduced by a throttling element. According to the disclosure, less charge air or no charge air is supplied, in order to reduce the exhaust and refill losses of the cylinders that have been switched off. In comparison with an unchanged charge air flow with the intake line fully open, the reduced charge air flow through the at least one cylinder that has been switched off leads to reduced heat transfer due to convection, with the result that the cylinders that have been switched off cool to a lesser extent or not at all during partial shutdown. This has advantages particularly as regards pollutant emissions, particularly as regards emissions of unburned hydrocarbons, since the cylinders that have been switched off re-attain or once again have the operating temperature thereof immediately after the ending of partial shutdown.
Systems and methods are provided herein for an engine wherein one group of cylinders is active and a second group of cylinders is switchable, such that under low loads the second group of cylinders is deactivated, and under high loads the second group of cylinders is activated. Following deactivation of the second group of cylinders a throttling element in an intake line for the second group of cylinders is gradually closed. The closing of the throttling element may reduce pumping losses and thus increase engine efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Further, the inventors herein have recognized the disadvantages noted herein, and do not admit them as known.